Alpha**5-o-acyl-pyridoxal derivatives

ABSTRACT

A-5-O-ACYL-PYRIDOXALS ACCORDING TO THE FORMULA   2-(CH3-),3-(HO-),4-(OHC-),5-(R-COO-CH2-)PYRIDINE   AND A METHOD OF MANUFACTURE THEREOF THEREOF BY OXIDATION OF THE CORRESPONDING A5-O-ACYL-PYRIDOXINE USING MANGANESE COMPOUNDS AS OXIDIZING AGENTS.

United States Patent 01 3,644,385 Patented Feb. 22, 1972 3,644,385 a-O-ACYL-PYRIDOXAL DERIVATIVES Isamu Utsumi, Kyoto-shi, Kyoto-fu, ToshiroWatanabe,

Takatsuki-shi, Osaka-fu, Keiichi Kohno, Toyonaka-slii, Osaka-fu, IsamuDaira, Kawanishi-shi, and Akira Otsubo, Kobe-shi, Japan, assignors toTanabe Seiyaku Co., Ltd., Osaka, Japan No Drawing. Filed Nov. 25, 1968,Ser. No. 778,793 Claims priority, appliigation Japan, Nov. 27, 1967,

US. Cl. 260295.5 R 3 Claims ABSTRACT OF THE DISCLOSURE 1x-O-acyl-pyridoxals according to the formula CH2OCOR and a method ofmanufacture thereof by oxidation of the corresponding a-O-acyl-pyridoxine using manganese compounds as oxidizing agents.

This invention relates to novel derivatives of pyridoxal. Moreparticularly, it relates to a -O-acyl-pyridoxal represented by theformula H0 CHzOC o R TABLE 2.TOTAL IYRIDOXAL CONCENTRATION (AND I INRATS, 1G. PERCENT penetrate into erythrocytes 2-3 times faster thanpyridoxal, and about 200 times faster than pyridoxal phosphate. Table 2shows that the administration of the above three u -O-acyl-pyridoxalcompounds to rats resulted in blood, liver and brain pyridoxal levelswhich were higher and longer maintained than pyridoxal levels obtainedafter the administration of known vitamin B compounds. Similar improvedcharacteristics are obtained with the corresponding acetyl, n-propionyl,n-varelyl, iso-varelyl, caproyl, heptanoyl, hexanoyl, palmitoyl ornicotinoyl groups.

The remarkable durability of certain of these compounds in the livingbody is dramatically demonstrated by Table 3 which shows the estimationof half life of these compounds in the blood of rabbits.

TABLE 1.-PERCE-NTAGES OF PENETRATED VIMMIN 11'500 gglggPOUNDS INTOERYTHROCYTE (TOTAL PYR-I- The compounds pyridoxal, pyridoxine, a-O-butyryl pyridoxine, pyridoxal-u phosphate, a -O-pyridoxal butyrate, a-O-pyridoxa1 isobutyrate and a -O-pyridoxal benzoate were each tested asfollows: The test compound was dispered in a 0.05 M phosphate bulfersolution (pH 7.4) in which erythrocytes, collected from 3 ml. of rabbitblood, were suspended. The resultant dispersion was shaken at 37 C. andthe increase in pyridoxal penetration into the erythrocyte was thenestimated. The results of these tests are set forth in Table 1 above,wherein Ht percent is the hematocrit value represented by volumepercentage of erythrocyte in its suspension, and ag/ml. cell is thatconcentration of the compound represented by the equivalent amount(,ug.) of pyridoxal hydrochloride in one m1. of blood cells.

YRIDOXAL PHOSPHATE CONCENTRATION) Route Intravenous Subcutaneous OralBlood Liver Brain Blood Liver Blood Liver After After After After AfterAfter Alter Compound Max. 3 hrs. Max. 3 hrs. Max. 3 hrs. Max. 3 hrs.Max. 3 hrs. Max. 3 hrs. Max. 3 hrs. 873 369 314 97 2,122 151 932 335 985243 901 49s Pyfldmal 21945 213 {(412 299 (153) 97) 417) 337) 21) 15 458374 Pyridml 835 514 353 182 2 788 310 865 474 1 139 174 1 002 427Pmsphate 11789 359 {(688) 435) (181) 109) (705 (421 (21 12 (452 333Pyridoxine 317 544 309 Pyridoxal ester! 752 05 37 303 Imbutymmflfl 2281,130 407) 403) (185) Butyrate 647 1 980 52 (396) Benzoate 1,150 600 076847 537 357 274 Nicotmate 50320 11042 415 377 132) ample, as illustratedin Table 1, a -O-n-butyryl-pyridoxal, a O isobutyryl-pyridoxal andJ-O-benzoyl-pyridoxal The compounds pyridoxal, pyridoxal phosphate,pyridoxine, pyridoxal isobutyrate, pyridoxal butyrate, pyridoxalbenzoate and pyridoxal nicotinate were each tested as follows: The testcompound was administered to rats intravenously, subcutaneously andorally, in the form of a solution adjusted to pH 7.4 with 0.1M-phosphatebuffer, said solution containing an amount equimolar to 10mg. of pyridoxal hydrochloride per kg. of body weight. Pyridoxal levelswere estimated With time. Mean values, of three animals for each group,were tabulated. Table 2, above, sets forth these results.

TABLE 3.I-IALF LIFE OF TOTAL PYRIDOXAL CONCEN- TRATION IN RABBIT BLOODThe compounds pyridoxal, pyridoxal phosphate, pyridoxal-u -butyrate andpyridoxal-a -isobutyrate were each tested as follows: The test compoundwas administered intravenously to rabbits in the form of a solutionadjusted to pH 7.4 with 0.1 M-phosphate buffer, said solution containingan amount equimolar to mg. of pyridoxal hydrochloride per kg. of bodyWeight, and the half life of total pyridoxal concentration in the blood(and velocity constant thereof) was calculated. Table 3, above, setsforth these results.

The compounds of the present invention are effective in relievingvitamin B deficiency symptoms in adult human beings when administeredorally in doses of about 30-l00 mg./day or intravenously in doses ofabout 10- 30 mg./ day. We have found that the M-O-acyl-pyridoxals arereadily hydrolyzable into pyridoxal in the living body. For example, wehave ascertained that 60% of the :1 benzoate, n-butyrate andiso-butyrate of yridoxal (when incubated in a 5% aqueous homogenate ofthe intestinal tract of rats at 37 C. and at pH 7.4) is hydrolyzed intopyridoxal within 30 minutes. (A one ml. solution containing an amount ofpyridoxal ester equimolar to 20 g. of pyridoxal hydrochloride was mixedwith one ml. of 5% intestinal homogenate.) The n-butyrate of pyridoxalhydrolyzed rapidly under these conditions with 80% of the ester beingconverted into pyridoxal within 30 minutes.

Rapid in vivo absorption of u -O-acy1-pyridoxa1 and conversion intopyridoxal in the living body was also experimentally demonstrated after,for example, the oral administration of a -O-benzoyl-pyridoxal to rats.In said experiment, an amount of a -O-benzoyl-pyridoxal equimolar to 10mg. of pyridoxal hydrochloride/kg. was administered orally to rats andthe concentrations of total pyridoxal, pyridoxal phosphate and unchanged11 -0- benzoyl-pyridoxal in blood and liver were assayed respectively.The results obtained are set forth in Table 4, below, in whichconcentrations are shown in 14g. percent calculated as pyridoxalhydrochloride. The mean value of three animals is listed for each group.

According to the present invention, the a -O-acylpyridoxal (1) can beprepared by oxidizing the corresponding u -O-acyl-pyridoxine.

Although various oxidizing agents are employable for this purpose,manganese compounds such as manganese dioxide or manganese sulfate arepreferred. It is also preferable to activate the manganese compound byheating it at about 220-250 C. for several hours prior to its use in theoxidation reaction. As the reaction solvent, an inert solvent, whichdoes not react with the oxidizing agent, such as chloroform, methylenechloride, etc. may be employed. The reaction may be carried out at roomtemperature. However, since this greatly prolongs the reaction time, itis preferred to carry out the reaction at an elevated temperature.

Examples of the starting a -O-acyl-pyridoxine are the compounds in whichsaid acyl group (-COR) is a lower aliphatic acyl group such as acetyl,n-propionyl, n-butyryl, iso-butyryl, n-varelyl, iso-varelyl, caproyl,heptanoyl, hexanoyl, palmitoyl, benzoyl or nicotinoyl group. The methodof preparing a -O-acyl-pyridoxal from a -O-acyl-pyridoxine isillustrated in the following examples. However, it should be understoodthat these examples are given merely by way of explanation, not oflimitation, and that numerous changes may be made in the details withoutdeparting from the spirit and the scope of the invention as hereinafterclaimed.

EXAMPLE 1 Preparation of the starting compound 2.1 g. of 05,3-O-isopropylidene-pyridoxine was dissolved in 15 ml. of absolutepyridine and 1.1 g. of nbutyryl chloride was added to said solution. Themixture was stirred at C. for 4 hours and then evaporated to dryness,under reduced pressure, on a water bath. 20 ml. of water was added tothe residue. The resultant aqueous mixture was neutralized with sodiumbicarbonate and extracted with chloroform. The chloroform layer waswashed with water. The chloroform extract was then evaporated to removethe solvent and the resultant residue was dissolved in a small quantityof methanol. The methanol solution was decolorized and evaporated toremove the methanol. 60 ml. of 9% aqueous solution of formic acid wasthen added to the remaining oil. This mixture was heated for 30 minutesat 80 C. and concentrated under reduced pressure. The remaining yellowoily substance was adsorbed on silica gel and developed with a mixedsolvent of chloroform and ethanol (15:1) whereby 1.2 g. of aO-n-butyryl-pyridoxine melting at 9698 C. was obtained as a colorlesscrystalline powder. This represented a yield of 50% of theoretical. Theinfrared absorption of this com pound Was found to be 1737 cm.--(e-steric carbonyl).

Analysis-Calculated for C H NO (percent): C, 60.24; H, 7.16; N, 5.85.Found (percent): C, 60.13; H, 7.20; N, 5.80.

Preparation of a -o-n-butyryl-pyridoxal 1.2 g. of a-O-n-butyryl-pyridoxine, 2.4 g. of manganese dioxide and 80 ml. ofchloroform were admixed and the mixture was stirred, at roomtemperature, for 24 hours. The mixture was then filtered and thecollected insoluble filtrate was washed with chloroform. The filtrateand the washings were incorporated and evaporated to remove chloroform.The remaining oily substance Was permitted to stand untilcrystallization took place, whereby a quantitative amount of a-O-n-butyryl-pyridoxal, melting at 45-46 C., was obtained.

Analysis.-Calculated for C H NO (percent): C, 60.75; H, 6.37; N, 5.90.Found (percent): C, 60.51; H, 6.55; N, 5.73.

EXAMPLE 2 2.4 g. of a -O-isobutyryl-pyridoxine was prepared andoxidized, as described in Example 1. 2.1 g. of a -O-iSO'butyryl-pyridoxal, melting at 48-49 C. (after recrystallization frompetroleum ether), were obtained as slightly yellowish plates.

Analysis.-Calculated for C H NO (percent): C, 60.75; H, 6.37; N, 5.90.Found (percent): C, 60.70; H, 6.39; N, 5.75.

EXAMPLE 3 150 mg. of u -O-palmitoyl-pyridoxine and 300 mg. of activatedmanganese dioxide were suspended in 50 ml. of chloroform and the mixturewas stirred at room temperature for 48 hours. The reaction mixture wasfiltered and the filtrate was concentrated. The resultant residue wasrecrystallized from a mixture of petroleum ether and ether whereby 125mg. of a -O-palmitoyl-pyridoxal were obtained as colorless scalesmelting at 7072 C.

Analysis.-Calculated for C H O N (percent): C, 71.07; H, 9.69; N, 3.45.Found (percent): C, 71.02; H, 9.73; N, 3.52.

EXAMPLE 4 2.7 g. of a -O-benzoyl-pyridoxine was prepared and oxidized,as described in Example 1. 2.5 g. of a -O-benzoy1- pyridoxal, melting at112-113 C., were obtained.

Analysis.-Calculated for C H NO (percent): C, 66.41; H, 4.83; N, 5.16.Found (percent): C, 66.38; H,

EXAMPLE 5 2.7 g. of L -O-DiCOtillOYl-PYI'idOXiHG, prepared as describedin Example 1, was suspended in 40 ml. of chloroform. 4.7 g. of manganesedioxide was added to the sus 6 pension and the mixture was stirred for48 hours. The mixture was filtered and the insoluble filtrate was washedwith chloroform. The filtrate and the washings were incorporated andevaporated to remove chloroform. The 5 residue was dissolved in acetoneand petroleum ether was added to the solution, whereby a quantitativeamount of a -O-nicotinoyl-pyridoxal melting at 142.2-143" C. wasobtained as slightly yellowish needles.

Analysis.Calculated for C H O N (percent): C, 61.76; H, 4.44; N, 10.29.Found (percent): C, 61.53; H,

What we claim is: 1. Pyridoxal-a -n-butyrate. 2.Pyridoxal-fi-isobutyrate.

15 3. Pyridoxal-a benzoate.

References Cited UNITED STATES PATENTS 2,955,115 10/1960 Kammerow et a1.260297 OTHER REFERENCES Kuroda et al.: Chem. Abstracts, vol. 66, No. 17,item No. 75 890m, Apr. 24, 1967.

ALAN L. ROTMAN, Primary Examiner US. Cl. X.R.

